1. Field of the Invention
The present invention relates to a DC current brushless motor driver apparatus using an inverter therein, and in particular, it relates to a DC current brushless motor driver apparatus and an air driven thereby, wherein a relative position (hereinafter, being called by xe2x80x9cmagnetic pole positionxe2x80x9d) between armature windings (stator windings) and stator windings is detected by a velocity or speed electromotive force which is induced across the stator windings, so as to control a revolution number thereof.
2. Description of Prior Art
As a conventional example of a DC brushless motor driving apparatus is described, for example in Japanese Patent Publication No. Sho 59-36519 (1984), wherein control of a revolution number thereof is conducted by detecting magnetic pole positions of a rotor, i.e., the relative positions between the magnetic rotor (herein after, being called only by a xe2x80x9crotorxe2x80x9d) and stator windings due to the velocity electromotive force (induction voltages) which is induced across the stator windings of the DC brushless motor.
In this, converting the induction voltages of three phases generated across the stator windings into three triangle-like signals, each having a positional relationship of around 90xc2x0 to each the induction voltage, those three triangle-like signals are conducted into resistors which are connected in a star-connection, so as to make comparisons between the voltage at a neutral point of the star-connection and those of the three triangle-like signals by comparators. And, a group of semiconductor switching elements, contracting an inverter therewith, are controlled corresponding to pulse signals obtained from those comparators, thereby rotating the DC brushless motor.
In the DC brushless motor according to this conventional art, the triangle-like signals, each having the phase difference of around 90xc2x0 to the each terminal voltage across each of the stator windings, are obtained by passing the terminal voltages of the stator windings through primary filters, however in this instance, the transfer function of the primary filters must be set so that the phase difference of around 90xc2x0 can be maintained within a predetermined range of a basic frequency of the induction voltages (being in relation with the revolution number of the motor). Also, when noises or the like, having frequencies being higher than the basic frequency of the induction voltages, cannot removed sufficiently therefrom by means of the primary filters, and then if it is impossible to obtain the triangle-like signal having smooth wave-form therewith, there are further added low pass filters so as to remove the high frequency signals, such as the noises or the like therefrom.
From the above pulse signals obtained in this manner, the relative position between the rotor and the stator windings are assumed or obtained, thereby it is possible to perform the control of rotation speed of the DC brushless motor depending upon a result of that assumption.
By the way, in the DC brushless motor driving apparatus according to the conventional technology mentioned above, the primary filters are used for the purpose of obtaining the triangle-like signals, each having a relationship in the phase of around 90xc2x0 to each of the induction voltages. Each of those filters, however, has a frequency characteristic that, when the basic frequency of the induction voltage as an input signal becomes low, the phase difference from the triangle-like signal which is obtained by this filter comes to be large. For the purpose of driving the DC brushless motor under a stable condition with good efficiency, there is a necessity that the frequency characteristic must be set, so that the phase difference of around 90xc2x0 is maintained within the predetermined range of the basic frequency of the induction voltages, however for example, in a case where the range of the basic frequency of the induction voltages is desirous to be extended or expanded (i.e., a variable range of revolution number of the DC brushless motor is desirous to be extended or expanded), there is a problem that it is impossible to maintain the phase difference between the induction voltage and the triangle-like signal at around 90xc2x0, depending upon the frequency characteristic of the filters.
Also, the terminal voltage of the DC brushless motor, as is shown in FIG. 2 of the Japanese Patent Publication No. Sho 59-36519 (1984), comes to be such that a spike wave-form is superposed upon a trapezoidal wave-form. And, the noises or the like, having the frequencies being higher than the basic frequencies of those spike wave-form and the induction voltage, cannot be removed sufficiently by means of the primary filters, and it is impossible to assume or obtain the relative position between the rotor and the stator windings with accuracy, if the triangle-like signal is not smooth in the wave-form thereof, then the low pass filter is added further more, at an output stage of the above-mentioned comparator for comparing the triangle-like signal and a reference signal, thereby to remove the high frequency signals, such as the noises or the like.
However, it is enough to make the time constant of the filter large for the purpose of smoothing the wave-form of the triangle-like signal, but it causes time delay in the signal, therefore there is an upper limit in setting of the time constant of the filters. By the way, in the DC brushless motor, the wave-form of the spike voltage is changed depending upon a load of the motor, but there is the upper limit in setting the time constant of the filters, then there is a problem that it is impossible to maintain the phase difference between the induction voltage and the triangle-like signal at 90xc2x0, since the phase of the triangle-like signal is fluctuated in an appearance thereof due to change in the wave-form of the triangle-like signal.
In this manner, when the filters are used for the purpose of assuming or obtaining the relative position between the rotor and the stator windings, the accuracy in assuming the relative relationship between the rotor and the stator windings is decreased down due to the limits in the frequency characteristic and in setting of the time constant of the filters, in particular when driving the DC brushless motor in a wide range of the revolution number, or when operating it under a load condition of wide range, therefore it is difficult to drive the DC brushless motor under the stable condition with good efficiency.
An object according to the present invention is, for dissolving such the problems mentioned in the above, to provide a DC brushless motor driving apparatus and an air conditioner driven thereby, being able to drive the DC brushless motor under stable condition with good efficiency, even in a case of driving the DC brushless motor in a wide range of the revolution number, or in a case of driving it under a wide range of the load condition.
Another object according to the present invention is, for dissolving such the problems mentioned in the above, to provide a DC brushless motor driving apparatus and an air conditioner driven thereby, being able to detect the commutation timings of a group of semiconductor switching elements of an inverter with certainty, when starting the DC brushless motor or operating it under a light load condition, thereby enabling a stable operation control thereof.
According to the present invention, for accomplishing the object mentioned above, in a DC brushless motor driving apparatus is provided a rotor magnetic pole position detecting circuit for generating magnetic pole position detecting signals for respective phases, by comparing three-phase induction voltages generated across the stator windings to a DC power source voltage of the inverter, in which a plurality of semiconductor switching elements are constructed in a star-connection, or to a reference voltage of a predetermined voltage obtained from a neutral point of said stator windings, wherein a timing for changing over a turn-on interval is obtained by referring to the magnetic pole position detecting signals with respect to any one of the stator windings which is not turned-on, thereby rotating the rotor.
Also, according to the present invention, the driving portion does not refer to said magnetic pole position detecting signal during a time when flywheel current flows through the flywheel diode.
Further, according to the present invention, the levels of the magnetic pole position detecting signals obtained from the above rotor magnetic pole position detecting circuit are detected sequentially, thereby to obtain the timing for changing from a changing time point of the level to a next turn-on interval.
Further, according to the present invention, for accomplishing the object mentioned above, there is provided means for making a frequency of PWM signals of inverter driving signals variable, thereby enabling to make the frequency of the PWM signals different, between when starting or driving the DC brushless under a light load and when driving a normal stable condition.
Also, according to the present invention, such the means is so constructed that the frequency of the PWM signals is exchanged when an ON of the PWM signal comes to be equal to a predetermined time which is set in advance.
Further, according to the present invention, the means mentioned above is so constructed that, detecting a DC power source voltage of the inverter, the frequency of the PWM signals is exchanged depending upon a result of the detection.